Patent GB-1269243-A (GB)
Title: Tightening and releasing tools in the spindle of a machine tool
IPC: B23B31/26
Filed: 1969-09-03
Abstract: 1,269,243. Draw-bar Operating. FRIEDRICH DECKEL PRAZISIONS MECHANIK & MASCHINENBAU. 3 Sept., 1969 [4 Sept., 1968], No. 43706/69. Heading B3T. A draw-bar operating mechanism in a machine tool comprises an electric motor 32 the rotor 40 of which is driving, by connected-through epicyclic gearing to the spindle 18 and to the draw bar 24, the epicyclic gearing including two sun-wheels 92, 98 and planet wheels 80 located in a planet carrier 68, 70 and which are housed in a two-part gear casing 56, 58 secured to the motor casing 38 and spindle 18 and which are rotatable in unison. When the spindle is started the gear casing 56, 58, motor casing 38, stator 34 and bearing flange 50 participate in the spindle rotation, the planet wheel carrier 68, 70 and its associated parts including the draw bar 24, pinion 52 and its associated parts including the flywheel 46 are entrained by the motion reversing gears 86. The polar moments of inertia of these two assemblies are arranged with respect to the pins 88 of the gears 86 are substantially equal. In consequence the pinion 52 and the planet wheel carrier 68, 70 remain in the same position relative to each other. In Fig. 3 the mechanism is shown in the tool-clamping position, rotation of the sleeve 102 on the bush 110 having caused the sleeve to be displaced to the right compressing the springs 104 thus applying a retracting force to the drawbar through the thrust bearing 106 and bush 94. If the rotor 40 of the tool clamp motor is now driven for releasing the tool it will transmit this rotation by way of pinion 52, the gear-wheels 86 and gear ring 84 to the planet wheel carrier 68, 70. Initially the sun-wheel 92 offers considerable resistance to being rotated due to friction between a tool and draw bar due to the spring force, the resistance offered by the sun-wheel 98 is lower due to the relationship between helix angle of the thread and friction coefficient between the tool and bar. When the planet carrier is driven the sun-wheels 92 will not at first rotate but the other sunwheel 98 will rotate causing the sleeve 102 to be displaced to the left on its bush 110 which releases the force of the spring 104. When the sleeve reaches its left hand position it is stopped by pin 112, the sun-wheel stops rotating whereupon the sun-wheel 92 can start to rotate. Due to the release of the springs 104 the torque required to turn the sun-wheel 92 is considerably reduced and the draw bar can easily be turned to unscrew the tool from the end thereof and the sun-wheel 92 therefore rotates in the opposite direction to that of the planet carrier 68, 70 and will turn the draw bar 24 to release the tool. When a fresh tool is inserted and tightened the operation is reversed. When the tool is drawn tightly into its socket in the spindle the clamping torque increases while the springs 104 are being compressed until the rotor 40 is braked upon reaching its limiting torque. The momentum of the flywheel 46 generates a final impetus for tightening the tool, the motor being switched off at this instant by the tripping of an overload relay.